Christian Hahnel

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PURPOSE Evaluation of a new method to visualize distribution and morphology of human corneal nerves (Adelta- and C-fibers) by means of fluorescence staining, confocal laser scanning microscopy, and 3-dimensional (3D) reconstruction. METHODS Trephinates of corneas with a diagnosis of Fuchs corneal dystrophy were sliced into layers of 200 microm thickness(More)
Polymer electrolyte membrane (PEM) fuel cell systems convert chemical energy from hydrogen into electrical power via a reaction with oxygen. Fuel cells are highly efficient, nearly noiseless, and locally emission-free. However, safe and efficient operation requires special system temperatures, mass flow rates of the reaction gases, and a particular excess(More)
• Background: Little is known about the spatial arrangement and the corresponding morphometric data describing the living keratocyte network. For determination of alterations in corneal diseases it is crucial to know the morphology of the keratocyte network in the healthy state. Porcine cornea was used as a model tissue because il allows the study of(More)
For an efficient chemical reaction and a safe operation for both stationary and dynamic loads all values of anode and cathode gas pressures and stack temperature must fall within specific ranges. System error can result in values outside of these ranges, in turn causing serious damage to the fuel cell (FC). In addition the energy supply by the FC is at(More)
This paper deals with an Optimal Iterative Learning Control approach for the anode pressure during the periodic purge processes of a fuel cell system. Due to accumulation of diffused nitrogen and water condensate inside the anode volume the chemical reaction is restrained. This adverse effect is avoided through the purge process, by which a short time(More)
Polymer-Elektrolyt-Membran-Brennstoffzellen (PEMBZ) sind in der Lage, die chemische Energie von Wasserstoff direkt in elektrische Energie unter Nutzung des Luftsauerstoffs zu wandeln. Für den Betrieb von PEMBZ-Systemen existieren verschiedene Möglichkeiten der Zufuhr und Nutzung des eingesetzten Wasserstoffs. Eine Möglichkeit ist der Rezirkulationsbetrieb.(More)
Of course, fuel cells are also subjects to signs of wear. Over time of usage this is shown by lower power efficiency, the degradation. Degradation correlates with wear due to mechanical stress, high stack temperature, and too fast load changes. Generally it is influenced by operating the fuel cell with wrong conditions regarding to temperature, anode and(More)
Sensitive systems in control approaches, such as fuel cells, require exact operating conditions for high efficiency, safety and endurance of the system. A promising method in controlling fuel cell systems is model predictive control (MPC). For those, many states have to be measured very precisely within high sampling rates, because they are used as initial(More)
Polymer electrolyte membrane (PEM) fuel cell (FC) systems convert chemical energy from hydrogen into electrical energy via a reaction with oxygen. FCs are highly efficient, nearly noiseless, and locally emission-free. An efficient and safe operation demands several variables in certain ranges. However, the electrical characteristic of a FC systems shows a(More)
In preceding papers we demonstrated an inhibitory effect of wheat germ agglutinin (WGA) and Ulex europaeus agglutinin (UEA) on the cholecystokinin (CCK) binding to the CCK receptor of rat pancreatic cells and also on the CCK induced Ca2+ release and alpha-amylase secretion in vitro as well as on pancreatic secretion of intact rats in vivo. In the present(More)
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